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19-3483; Rev 0; 11/04
KIT ATION EVALU E AILABL AV
Dual PCI Express, Hot-Plug Controller
General Description Features
PCI Express Compliant Hot Swaps 12V, 3.3V, and 3.3V Auxiliary for 2 PCI-E Slots Integrated Power MOSFET for Auxiliary Supply Rails Controls dI/dt and dV/dt Active Current Limiting Protects Against Overcurrent/Short-Circuit Conditions Programmable Current-Limit Timeout PWRGD Signal Outputs with Programmable Power-On Reset (POR) (160ms Default) Latched FAULT Signal Output after Overcurrent or Overtemperature Fault Attention Switch Inputs/Outputs with 4ms Debounce Present-Detect Inputs Forced-On Inputs Facilitates Testing Thermal Shutdown Allows Control through SMBus with an I/O Expander
MAX5946
Applications
Servers Desktop Mobile Server Platforms Workstations Embedded Devices
PRES-DETA FONA ONA AUXONA 12SA+ 12SA12GA 3.3SA+ 3.3SA1 2 3 4 5 6 7 8 9
36 35 34 33 32 31 30 29 28
PGND GND
TOP VIEW
12VIN INPUT1 OUTPUT1 OUTPUT2 INPUT2 TIM
PORADJ
The MAX5946 dual hot-plug controller is designed for PCI ExpressTM applications. The device provides hotplug control for 12V, 3.3V, and 3.3V auxiliary supplies of two PCI express slots. The MAX5946's logic inputs/outputs allow interfacing directly with the system hot-plug management controller or through an SMBusTM with an external I/O expander. An integrated debounced attention switch and present-detect signals are included to simplify system design. The MAX5946 drives four external n-channel MOSFETs to control the 12V and 3.3V main outputs. The 3.3V auxiliary outputs are controlled through internal 0.3 n-channel MOSFETs. Internal charge pumps provide gate drive for the 12V outputs while the gate drive of the 3.3V output is driven by the 12V input supply. The 3.3V auxiliary outputs are completely independent from the main outputs with their own charge pumps. At power-up, the MAX5946 keeps all of the external MOSFETs off until the supplies rise above their respective undervoltage lockout (UVLO) thresholds. The device keeps the internal MOSFETs off only until the auxiliary input supply rises above its UVLO threshold. Upon a turn-on command, the MAX5946 enhances the external and internal MOSFETs slowly with a constant gate current to limit the power-supply inrush current. The MAX5946 actively limits the current of all outputs at all times and shuts down if an overcurrent condition persists for longer than a programmable overcurrent timeout. Thermal-protection circuitry also shuts down all outputs if the die temperature exceeds +150C. After an overcurrent or overtemperature fault condition, the MAX5946L latches off while the MAX5946A automatically restarts after a restart time delay. The device is available in a 36-pin (6mm x 6mm) thin QFN package and operates over the -40C to +85C temperature range.
Ordering Information
PART MAX5946AETX MAX5946LETX TEMP RANGE -40C to +85C -40C to +85C PIN-PACKAGE 36 Thin QFN 36 Thin QFN
Pin Configuration
27 26 25 24
PRES-DETB FONB ONB AUXONB 12SB+ 12SB12GB 3.3SB+ 3.3SB-
MAX5946
23 22 21 20 19
10 11 12 13 14 15 16 17 18
FAULTA PWRGDA 3.3VAUXOA 3.3VAUXIN 3.3VAUXOB PWRGDB
FAULTB
3.3GA
SMBus is a trademark of Intel Corp. PCI Express is a trademark of PCI-SIG Corp.
THIN QFN
________________________________________________________________ Maxim Integrated Products
3.3GB
Typical Application Circuit appears at end of data sheet.
1
For pricing, delivery, and ordering information, please contact Maxim/Dallas Direct! at 1-888-629-4642, or visit Maxim's website at www.maxim-ic.com.
Dual PCI Express, Hot-Plug Controller MAX5946
ABSOLUTE MAXIMUM RATINGS
(All voltages referenced to GND, unless otherwise noted.) 12VIN......................................................................-0.3V to +14V 12GA, 12GB ..............................................-0.3V to (V12VIN + 6V) 12SA+, 12SA-, 12SB+, 12SB-, 3.3GA, 3.3GB .....................................-0.3V to (V12VIN + 0.3V) 3.3VAUXIN, ONA, ONB, FAULTA, FAULTB ............-0.3V to +6V PWRGDA, PWRGDB ................................................-0.3V to +6V PGND ....................................................................-0.3V to +0.3V All Other Pins to GND......................-0.3V to (V3.3VAUXIN + 0.3V) Continuous Power Dissipation (TA = +70C) 36-Pin Thin QFN (derate 26.3mW/C above +70C).....2.105W Operating Temperature Range ...........................-40C to +85C Junction Temperature ......................................................+150C Storage Temperature Range .............................-65C to +150C Lead Temperature (soldering, 10s) .................................+300C
Stresses beyond those listed under "Absolute Maximum Ratings" may cause permanent damage to the device. These are stress ratings only, and functional operation of the device at these or any other conditions beyond those indicated in the operational sections of the specifications is not implied. Exposure to absolute maximum rating conditions for extended periods may affect device reliability.
ELECTRICAL CHARACTERISTICS
(V12VIN = V12S_- = V12S_+ = 12V, V3.3S_+ = V3.3S_- = V3.3VAUXIN = VON_ = VAUXON_ = VFON__ = 3.3V, PWRGD_ = FAULT_ = PORADJ = TIM = OUTPUT_ = 12G_ = 3.3G_ = OPEN, INPUT_ = PRES_DET_ = PGND = GND, TA = -40C to +85C, unless otherwise noted. Typical values are at TA = +25C.) (Note 1)
PARAMETER 12V SUPPLY 12V Supply Voltage Range 12VIN Undervoltage Lockout 12VIN Supply Current 12VIN CONTROL 12VIN Current-Limit Threshold (V12S_+ - V12S_-) 12G_ Gate Charge Current 12G_ Gate Discharge Current 12G_ Gate High Voltage (V12G_ - V12VIN) 12G_ Threshold Voltage For PWRGD_ Assertion (Note 2) 12S_- Input Bias Current 12S_+ Input Bias Current 3.3V SUPPLY 3.3V Supply Voltage Range Undervoltage Lockout (Note 3) V3.3SA+, V3.3SB+ 3.3SA+ rising Hysteresis 3.0 2.52 3.3 2.65 30 3.6 2.78 V V mV 20 V12ILIM I12G_CHG I12G_DIS V12G_ = GND Normal turn-off, ON_ = GND, V12G_ = 2V Output short-circuit condition, strong gate pulldown to regulation, V12VIN - V12S_ 1V, V12G_= 5V I12G_ = 1A Referred to V12VIN, I12G_ = 1A 49 4 50 50 4.8 -3.0 54 5 150 120 5.3 -4 59 6 250 180 5.8 -4.8 1 60 mV A A mA V V A A V12VIN V12UVLO I12VIN 10.8 12 10 0.1 0.5 1 13.2 10.5 V V mA SYMBOL CONDITIONS MIN TYP MAX UNITS
V12VIN rising
Hysteresis V12VIN = 13.2V
9.5
V12G_H VPGTH12
2
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Dual PCI Express, Hot-Plug Controller
ELECTRICAL CHARACTERISTICS (continued)
(V12VIN = V12S_- = V12S_+ = 12V, V3.3S_+ = V3.3S_- = V3.3VAUXIN = VON_ = VAUXON_ = VFON__ = 3.3V, PWRGD_ = FAULT_ = PORADJ = TIM = OUTPUT_ = 12G_ = 3.3G_ = OPEN, INPUT_ = PRES_DET_ = PGND = GND, TA = -40C to +85C, unless otherwise noted. Typical values are at TA = +25C.) (Note 1)
PARAMETER 3.3V CONTROL 3.3V Current-Limit Threshold (V3.3S_+ - V3.3S_-) 3.3G_ Gate Charge Current 3.3G_ Gate Discharge Current 3.3G_ Gate High Voltage (V3.3G_ - V3.3S_+) 3.3G_ Threshold Voltage For PWRGD_ Assertion (Note 2) 3.3S_- Input Bias Current 3.3S_+ Input Bias Current 3.3V AUXILIARY SUPPLY 3.3VAUXIN Supply Voltage Range 3.3VAUXIN Undervoltage Lockout 3.3VAUXIN Supply Current 3.3VAUXIN to 3.3VAUXO_ Maximum Dropout 3.3VAUXO_ Current-Limit Threshold 3.3VAUXO_ Threshold For PWRGD_ Assertion (V3.3VAUXIN - V3.3VAUXO_) (Note 3) LOGIC SIGNALS Input-Logic Threshold (ON_, FON_, AUXON_, PRES-DET_, INPUT_) Input Bias Current (ON_, AUXON_, INPUT_) FON_, PRES-DET_ Internal Pullup ON_, AUXON_ High-to-Low Deglitch Time 25 50 4 Rising edge Hysteresis 1.0 25 1 75 2.0 V mV A k s V3.3VAUXIN V3.3VAUXUVLO 3.3VAUXIN rising Hysteresis V3.3VAUXIN = 3.6V I3.3VAUXO_ = 375mA 3.3VAUXO_ shorted to GND 376 470 3.0 2.52 3.3 2.65 30 1.5 3 225 564 3.6 2.78 V V mV mA mV mA 20 V3.3ILIM I3.3G_CHG I3.3G_DIS V3.3G_ = GND ON_ = GND, V3.3G_ = 2V Output short-circuit condition, strong gate pulldown to regulation, V3.3S_+ - V3.3S_ 1V, V3.3G_ = 5V Sourcing 1A Referred to V3.3VAUXIN, I3.3G_ = 1A 17 4 50 100 4.5 -3.0 20 5 150 150 5.5 -4 23 6 250 220 6.8 -4.5 1 60 mV A A mA V V A A SYMBOL CONDITIONS MIN TYP MAX UNITS
MAX5946
V3.3G_H VPGTH3.3
VPGTH3.3AUX
400
mV
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3
Dual PCI Express, Hot-Plug Controller MAX5946
ELECTRICAL CHARACTERISTICS (continued)
(V12VIN = V12S_- = V12S_+ = 12V, V3.3S_+ = V3.3S_- = V3.3VAUXIN = VON_ = VAUXON_ = VFON__ = 3.3V, PWRGD_ = FAULT_ = PORADJ = TIM = OUTPUT_ = 12G_ = 3.3G_ = OPEN, INPUT_ = PRES_DET_ = PGND = GND, TA = -40C to +85C, unless otherwise noted. Typical values are at TA = +25C.) (Note 1)
PARAMETER PRES-DET_ High-to-Low Deglitch Time PWRGD_ Power-On Reset Time (Note 2) PWRGD_ Low-to-High Deglitch Time PWRGD_, FAULT_ Output Low Voltage PWRGD_, FAULT_ OutputHigh Leakage Current SYMBOL tDEG PORADJ = open tPOR_HL RPORADJ = 20k RPORADJ = 100k RPORADJ = 200k tPOR_LH Sinking 2mA Sinking 30mA VPWRGD_ = VFAULT_ = 5.5V TIM = open FAULT_ Timeout tFAULT RTIM = 15k RTIM = 120k RTIM = 300k FAULT_ Timeout During Startup Autorestart Delay Time Fault Reset Minimum Pulse Width (Note 4) Thermal-Shutdown Threshold Thermal-Shutdown Threshold Hysteresis OUTPUT_ Debounce Time OUTPUT_ High Voltage OUTPUT_ Low Voltage tDBC Sourcing 2mA Sinking 2mA 2.6 tSU tRESTART tRESET TSD TJ rising 5.5 1.4 12 11 2.6 22 59 2 x tFAULT 64 x tFAULT 100 +150 20 4.4 6.2 ms ms s C C ms V V CONDITIONS MIN 3 90 35 145 TYP 5 160 55 265 570 4 0.1 0.7 1 17.0 3.8 32 ms s V A MAX 7 250 75 380 ms UNITS ms
V3.3VAUXIN V3.3VAUXIN - 0.3 0.4
Note 1: Note 2: Note 3: Note 4:
100% production tested at TA = +25C. Parameters over temperature are guaranteed by design. PWRGD_ asserts a time tPOR_HL after VPGTH12, VPGTH3.3, and VPGTH3.3AUX conditions are met. The UVLO for the 3.3V supply is sensed at 3.3SA+. This is the time that ON_ or AUXON_ must stay low when resetting a fault condition.
4
_______________________________________________________________________________________
Dual PCI Express, Hot-Plug Controller
Typical Operating Characteristics
(V12VIN = V12SA+ = 12V, V3.3VAUXIN = V3.3S_+ = VON_ = VAUXON_ = VINPUT_ = 3.3V, PRES-DET_ = GND, FON_ = PORADJ = TIM = float, FAULT_ = 10k to 3.3VAUXIN, PWRGDA = 10k to 3.3VAUXO_, TA = +25C, unless otherwise noted, see the Typical Application Circuit.)
12VIN INPUT SUPPLY CURRENT vs. TEMPERATURE
0.505 0.504 0.503 0.502 0.501 0.500 0.499 0.498 0.497 0.496 0.495 0.494 0.493 0.492 0.491 0.490 -40 -15 10 35 60 TEMPERATURE (C)
MAX5946 toc01
MAX5946
3.3VAUXIN SUPPLY CURRENT vs. TEMPERATURE
MAX5946 toc02
ON AND AUXON LOW-TO-HIGH THRESHOLD VOLTAGE vs. TEMPERATURE
1.9 THRESHOLD VOLTAGE (V) 1.8 1.7 1.6 1.5 1.4 1.3 1.2 1.1 1.0 ON_ OR AUXON_
MAX5946 toc03
2.0 1.8 1.6 SUPPLY CURRENT (mA) 1.4 1.2 1.0 0.8 0.6 0.4 0.2 0
2.0
SUPPLY CURRENT (mA)
85
-40
-15
10
35
60
85
-40
-15
10
35
60
85
TEMPERATURE (C)
TEMPERATURE (C)
3.3VAUXO_ OUTPUT VOLTAGE vs. CURRENT
MAX5946 toc04
12G_ AND 3.3G_ GATE CHARGE CURRENT vs. TEMPERATURE
MAX5946 toc05
12G_ AND 3.3G_ GATE DISCHARGE CURRENT vs. TEMPERATURE
MAX5946 toc06
3.5 3.0 OUTPUT VOLTAGE (V) 2.5 2.0 1.5 1.0 0.5 0 0 0.1 0.2 0.3 0.4 0.5
5.35 5.30 GATE CHARGE CURRENT (A) 5.25 5.20 5.15 5.10 5.05 5.00 4.95 4.90 4.85 3.3G_ 12G_
170 GATE DISCHARGE CURRENT (A)
165 3.3G_ 160
155 12G_ 150
145 -40 -15 10 35 60 85 -40 -15 10 35 60 85 TEMPERATURE (C) TEMPERATURE (C)
0.6
OUTPUT CURRENT (A)
3.3VAUX INTERNAL SWITCH MAXIMUM DROPOUT vs. TEMPERATURE
MAX5946 toc07
12V AND 3.3V CURRENT-LIMIT THRESHOLD VOLTAGE vs. TEMPERATURE
MAX5946 toc08
AUXILIARY CURRENT LIMIT vs. TEMPERATURE
0.495 AUXILIARY CURRENT LIMIT (A) 0.490 0.485 0.480 0.475 0.470 0.465 0.460 0.455
MAX5946 toc09
0.18 0.16 DROPOUT VOLTAGE (V) 0.14 0.12 0.10 0.08 0.06 0.04 0.02 0 -40
AUXILIARY OUTPUT CURRENT = 375mA
CURRENT-LIMIT THRESHOLD VOLTAGE (mV)
0.20
60 50 40 30 20 10 0 12V CURRENT-SENSE THRESHOLD
0.500
3.3V CURRENT-SENSE THRESHOLD
0.450 -40 -15 10 35 60 85 -40 -15 10 35 60 85 TEMPERATURE (C) TEMPERATURE (C)
-15
10
35
60
85
TEMPERATURE (C)
_______________________________________________________________________________________
5
Dual PCI Express, Hot-Plug Controller MAX5946
Typical Operating Characteristics (continued)
(V12VIN = V12SA+ = 12V, V3.3VAUXIN = V3.3S_+ = VON_ = VAUXON_ = VINPUT_ = 3.3V, PRES-DET_ = GND, FON_ = PORADJ = TIM = float, FAULT_ = 10k to 3.3VAUXIN, PWRGDA = 10k to 3.3VAUXO_, TA = +25C, unless otherwise noted, see the Typical Application Circuit.)
12VIN UNDERVOLTAGE LOCKOUT THRESHOLD vs. TEMPERATURE
MAX5946 toc10
3.3VAUXIN UNDERVOLTAGE LOCKOUT THRESHOLD vs. TEMPERATURE
MAX5946 toc11
10.20 10.15 UVLO THRESHOLD (V) 10.10 10.05 10.00 9.95 9.90
2.70
2.68 UVLO THRESHOLD (V)
2.66
2.64
2.62 9.85 9.80 -40 -15 10 35 60 85 TEMPERATURE (C) 2.60 -40 -15 10 35 60 85 TEMPERATURE (C)
12V TURN-ON/OFF TIME
MAX5946 toc12
3.3V TURN-ON/OFF TIME
MAX5946 toc13
12V OUTPUT 10V/div
3.3V OUTPUT 5V/div 3.3G_ 10V/div
12G_ 20V/div ON_ 5V/div
ON_ 5V/div
PWRGD_ 5V/div 40ms/div 40ms/div
PWRGD_ 5V/div
3.3V AUXILIARY TURN-ON/OFF TIME
MAX5946 toc14
12V POWER-UP
MAX5946 toc15
3.3AUXO_ OUTPUT VOLTAGE 2V/div
12G_ 20V/div 12V OUTPUT 10V/div
PWRGD 2V/div
12VIN, 12V INPUT 10V/div
AUXON_ 2V/div
PWRGD_ 5V/div 40ms/div
40ms/div
6
_______________________________________________________________________________________
Dual PCI Express, Hot-Plug Controller MAX5946
Typical Operating Characteristics (continued)
(V12VIN = V12SA+ = 12V, V3.3VAUXIN = V3.3S_+ = VON_ = VAUXON_ = VINPUT_ = 3.3V, PRES-DET_ = GND, FON_ = PORADJ = TIM = float, FAULT_ = 10k to 3.3VAUXIN, PWRGDA = 10k to 3.3VAUXO_, TA = +25C, unless otherwise noted, see the Typical Application Circuit.)
3.3V INPUT/3.3V AUXILIARY INPUT POWER-UP
MAX5946 toc16
TURN-ON DELAY 3.3V OUTPUT AND 3.3V AUXILIARY OUTPUT
MAX5946 toc17
3.3G_ 10V/div 3.3V OUTPUT 5V/div 3.3S_+ 5V/div 3.3VAUXO_ 5V/div PWRGD_ 5V/div 100ms/div
5V/div
3.3VAUXO_ OUTPUT VOLTAGE 3.3 INPUT, 3.3VAUXIN 3.3 OUTPUT VOLTAGE PWRGD 3.3G_
5V/div 5V/div 5V/div 10V/div
4ms/div
FAULT CONDITION ON 12V OUTPUT (AUTORESTART OPTION MAX5946A)
MAX5946 toc18
FAULT CONDITION ON 3.3V OUTPUT (AUTORESTART OPTION MAX5946A)
MAX5946 toc19
RLOAD STEP TO 1.5
12V OUTPUT CURRENT 5A/div 12G_ 20V/div 12V OUTPUT VOLTAGE 10V/div
RLOAD STEP TO 0.5
3.3V MAIN OUTPUT CURRENT 2A/div 3.3G_ 10V/div 3.3V OUTPUT VOLTAGE 5V/div
tRESTART 100ms/div
FAULT_ 5V/div
tRESTART 100ms/div
FAULT_ 5V/div
FAULT CONDITION ON AUXILIARY OUTPUT (AUTORESTART OPTION MAX5946A)
MAX5946 toc20
FAULT CONDITION ON 12V OUTPUT (LATCH OPTION MAX5946L)
MAX5946 toc21
RLOAD STEP TO 4
3.3VAUXO_ OUTPUT CURRENT 500mA/div
RLOAD STEP TO 1.5
12V OUTPUT CURRENT 5A/div 12G_ 20V/div
3.3VAUXO_ OUTPUT VOLTAGE 2V/div
12V OUTPUT VOLTAGE 10V/div
tRESTART 100ms/div
FAULT_ 2V/div 100ms/div
FAULT_ 5V/div
_______________________________________________________________________________________
7
Dual PCI Express, Hot-Plug Controller MAX5946
Typical Operating Characteristics (continued)
(V12VIN = V12SA+ = 12V, V3.3VAUXIN = V3.3S_+ = VON_ = VAUXON_ = VINPUT_ = 3.3V, PRES-DET_ = GND, FON_ = PORADJ = TIM = float, FAULT_ = 10k to 3.3VAUXIN, PWRGDA = 10k to 3.3VAUXO_, TA = +25C, unless otherwise noted, see the Typical Application Circuit.)
FAULT CONDITION ON 3.3V OUTPUT (LATCH OPTION MAX5946L)
MAX5946 toc23
FAULT CONDITION ON 12V OUTPUT
MAX5946 toc22
tFAULT
RLOAD STEP TO 1.5
12V OUTPUT CURRENT 5A/div 12G_ 20V/div 12V OUTPUT VOLTAGE 10V/div
RLOAD STEP TO 0.5
3.3V OUTPUT CURRENT 2A/div 3.3G_ 10V/div 3.3V OUTPUT VOLTAGE 5V/div
FAULT_ 5V/div 4ms/div 100ms/div
FAULT_ 5V/div
FAULT CONDITION ON 3.3V MAIN OUTPUT
MAX5946 toc24
FAULT CONDITION ON AUXILIARY OUTPUT (LATCH OPTION MAX5946L)
MAX5946 toc25
tFAULT
RLOAD STEP TO 0.5
3.3V OUTPUT CURRENT 2A/div 3.3G_ 10V/div 3.3V OUTPUT VOLTAGE 5V/div
RLOAD STEP TO 4
3.3VAUXO_ OUTPUT CURRENT 500mA/div
3.3VAUXO_ OUTPUT VOLTAGE 2V/div FAULT_ 2V/div 100ms/div
FAULT_ 5V/div 4ms/div
FAULT CONDITION ON AUXILIARY OUTPUT
MAX5946 toc26
SHORT CIRCUIT ON 12V OUTPUT
MAX5946 toc27
tFAULT
RLOAD STEP TO 4
3.3VAUXO_ OUTPUT CURRENT 500mA/div
12V OUTPUT CURRENT 5A/div 12G_ 20V/div
3.3VAUXO_ OUTPUT VOLTAGE 2V/div FAULT_ 2V/div 4ms/div 2ms/div
12V OUTPUT VOLTAGE 10V/div
FAULT_ 5V/div
8
_______________________________________________________________________________________
Dual PCI Express, Hot-Plug Controller MAX5946
Typical Operating Characteristics (continued)
(V12VIN = V12SA+ = 12V, V3.3VAUXIN = V3.3S_+ = VON_ = VAUXON_ = VINPUT_ = 3.3V, PRES-DET_ = GND, FON_ = PORADJ = TIM = float, FAULT_ = 10k to 3.3VAUXIN, PWRGDA = 10k to 3.3VAUXO_, TA = +25C, unless otherwise noted, see the Typical Application Circuit.)
SHORT CIRCUIT ON 12V OUTPUT
MAX5946 toc28
SHORT CIRCUIT ON 3.3V OUTPUT
MAX5946 toc29
12V OUTPUT CURRENT 25A/div 12G_ 20V/div 0V 12V OUTPUT VOLTAGE 10V/div 0V FAULT_ 5V/div 0V 4s/div 2ms/div
3.3V OUTPUT CURRENT 2A/div
3.3G_ 5V/div 3.3V OUTPUT VOLTAGE 5V/div FAULT_ 5V/div
SHORT CIRCUIT ON 3.3V OUTPUT
MAX5946 toc30
SHORT CIRCUIT ON 3.3AUXO_
MAX5946 toc31
3.3V OUTPUT CURRENT 10A/div
3.3VAUXO_ OUTPUT CURRENT 500mA/div
3.3G_ 5V/div 3.3V OUTPUT VOLTAGE 5V/div FAULT_ 5V/div 0V 2s/div 2ms/div
3.3VAUXO_ OUTPUT VOLTAGE 2V/div
FAULT_ 5V/div
SHORT CIRCUIT ON 3.3VAUXO_
MAX5946 toc32
POWER-UP INTO FAULT (AUXILIARY SUPPLY)
MAX5946 toc33
RLOAD = 4 3.3VAUXO_ OUTPUT CURRENT 5A/div tSU 3.3VAUXO_ OUTPUT CURRENT 500mA/div 3.3VAUXO_ OUTPUT VOLTAGE 2V/div
3.3VAUXO_ OUTPUT VOLTAGE 2V/div
AUXON_ 5V/div FAULT_ 5V/div 2s/div FAULT_ 5V/div 4ms/div
_______________________________________________________________________________________
9
Dual PCI Express, Hot-Plug Controller MAX5946
Typical Operating Characteristics (continued)
(V12VIN = V12SA+ = 12V, V3.3VAUXIN = V3.3S_+ = VON_ = VAUXON_ = VINPUT_ = 3.3V, PRES-DET_ = GND, FON_ = PORADJ = TIM = float, FAULT_ = 10k to 3.3VAUXIN, PWRGDA = 10k to 3.3VAUXO_, TA = +25C, unless otherwise noted, see the Typical Application Circuit.)
POWER-UP INTO FAULT (3.3V MAIN)
MAX5946 toc34
POWER-UP INTO FAULT (12V OUTPUT)
MAX5946 toc35
RLOAD = 0.5 tSU 3.3V OUTPUT CURRENT 4A/div 3.3G_ 5V/div 3.3V OUTPUT VOLTAGE 2V/div ON_, AUXON_ 5V/div FAULT_ 5V/div 4ms/div 4ms/div tSU 12V OUTPUT CURRENT 5A/div 12G_ 10V/div 12V OUTPUT VOLTAGE 10V/div ON_, AUXON_ 5V/div FAULT_ 5V/div
PRESENT-DETECT (ON/OFF) OPERATION
MAX5946 toc36
PRESENT-DETECT (ON/OFF) OPERATION
MAX5946 toc37
10V/div
12V OUTPUT VOLTAGE
10V/div
12V OUTPUT VOLTAGE
5V/div 5V/div
3.3VAUXO_ OUTPUT VOLTAGE PWRGD
5V/div 5V/div
3.3VAUXO_ OUTPUT VOLTAGE PWRGD
5V/div
PRES-DET_
5V/div
PRES-DET_
40ms/div
4ms/div
FORCED-ON (ON/OFF) OPERATION
MAX5946 toc38
FORCED-ON (ON/OFF) OPERATION
MAX5946 toc39
10V/div
12V OUTPUT VOLTAGE
10V/div
12V OUTPUT VOLTAGE
5V/div 5V/div
3.3VAUXO_ OUTPUT VOLTAGE PWRGD
5V/div 5V/div
3.3VAUXO_ OUTPUT VOLTAGE PWRGD
5V/div
FON_
5V/div
FON_
40ms/div
4ms/div
10
______________________________________________________________________________________
Dual PCI Express, Hot-Plug Controller MAX5946
Typical Operating Characteristics (continued)
(V12VIN = V12SA+ = 12V, V3.3VAUXIN = V3.3S_+ = VON_ = VAUXON_ = VINPUT_ = 3.3V, PRES-DET_ = GND, FON_ = PORADJ = TIM = float, FAULT_ = 10k to 3.3VAUXIN, PWRGDA = 10k to 3.3VAUXO_, TA = +25C, unless otherwise noted, see the Typical Application Circuit.)
POWER-ON-RESET TIME vs. PORADJ RESISTOR
3000 2800 2600 2400 2200 2000 1800 1600 1400 1200 1000 800 600 400 200 0 RPORADJ (k)
MAX5946 toc41
DEBOUNCED ON/OFF OPERATION
MAX5946 toc40
INPUT_ 2V/div tPOR_HL (ms) OUTPUT_ 2V/div
10ms/div
0 100 200 300 400 500 600 700 800 900 1000
tFAULT TIME DELAY vs. TIM RESISTOR
180 160 140 tFAULT (ms) 120 100 80 60 40 20 0 0 100 200 300 400 500 600 700 800 900 1000 RTIM (k)
MAX5946 toc42
200
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11
Dual PCI Express, Hot-Plug Controller MAX5946
Pin Description
PIN NAME FUNCTION Present-Detect Input A. PRES-DETA accepts inputs from the PRSNT#2 pin on a PCI express connector. PRES-DETA has an internal pullup to 3.3VAUXIN. When PRES-DETA is low, the outputs follow the command from ONA and AUXONA after a 4ms debounced time. When PRES-DETA goes from low to high, all outputs of the respective slot shut down with no delay (see Table 2). Forced-On Input A. FONA has a 50k internal pullup to 3.3VAUXIN. A logic-low on FONA turns on all slot A outputs as long as the power inputs are within their operating range, regardless of the status of the other input signals. Leave FONA open for normal operation (see Table 2). Slot A 12V And 3.3V Outputs Enable. A logic-high at ONA turns on the 12V and 3.3V outputs of slot A (see Table 2). Slot A 3.3V Auxiliary Output Enable. A logic-high at AUXONA turns on the slot A auxiliary output (3.3VAUXOA), see Table 2. Slot A 12V Positive Current-Sense Input. Connect the positive terminal of the current-sense resistor to 12SA+ using the Kelvin-sensing technique to assure accurate current sensing. Slot A 12V Negative Current-Sense Input. Connect 12SA- to the negative side of the current-sense resistor using the Kelvin-sensing technique to assure accurate current sensing. Slot A 12V Gate-Drive Output. Connect 12GA to the gate of slot A's 12V MOSFET. At power-up, V12GA is raised to the internal charge-pump voltage level by a constant current. Slot A 3.3V Positive Current-Sense Input. Connect the positive side of the current-sense resistor to 3.3SA+ using the Kelvin-sensing technique to assure accurate current sensing. This input is also used for the 3.3V supply's UVLO function. Slot A 3.3V Negative Current-Sense Input. Connect to the negative side of the sense resistor using the Kelvin-sensing technique to assure accurate current sensing. Slot A 3.3V Gate-Drive Output. Connect 3.3GA to the gate of slot A's 3.3V MOSFET. At power-up, V3.3GA is charged to 5.5V above the 3.3V supply by a constant current derived from V12VIN. Open-Drain Fault Output Signal. FAULTA latches active low whenever the slot A outputs are shut down due to a fault. A fault is either of: * An overcurrent condition lasting longer than the overcurrent timeout. * A device over temperature condition. If the fault is detected in the main outputs, FAULTA must be reset by toggling the ONA input. If the fault is in the auxiliary output, FAULTA must be reset by toggling both ONA and AUXONA. For the autorestart version, FAULTA is reset when the part initiates the next power-on cycle. Open-Drain Power-Good Output. PWRGDA goes low tPOR_HL after all outputs of slot A reach their final value and the power MOSFETs are fully enhanced. Slot A 3.3V Auxiliary Power-Supply Output 3.3V Auxiliary Supply Input. 3.3VAUXIN is the input to a charge pump that drives the internal MOSFETs connecting 3.3VAUXIN to 3.3VAUXOA and 3.3VAUXOB. V3.3VAUXIN is also used to power the internal control logic and analog references of the MAX5946. Slot B 3.3V Auxiliary Power Output Slot B Power-Good Output. See PWRGDA function. Slot B Open-Drain Fault Output. See FAULTA function. Slot B 3.3V Gate-Drive Output. See 3.3GA function.
1
PRES-DETA
2
FONA
3 4 5 6 7
ONA AUXONA 12SA+ 12SA12GA
8
3.3SA+
9 10
3.3SA3.3GA
11
FAULTA
12 13 14 15 16 17 18
PWRGDA 3.3VAUXOA 3.3VAUXIN 3.3VAUXOB PWRGDB FAULTB 3.3GB
12
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Dual PCI Express, Hot-Plug Controller
Pin Description (continued)
PIN 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 NAME 3.3SB3.3SB+ 12GB 12SB12SB+ AUXONB ONB FONB PRES-DETB TIM INPUT2 OUTPUT2 OUTPUT1 INPUT1 12VIN GND PGND PORADJ FUNCTION Slot B 3.3V Negative Current-Sense Input. See 3.3SA- function. Slot B 3.3V Positive Current-Sense Input. Connect the positive side of the current-sense resistor to 3.3SB+ using the Kelvin-sensing technique to assure accurate current sensing. Slot B 12V Gate-Drive Output. See 12GA function. Slot B 12V Negative Current-Sense Input. See 12SA- function. Slot B 12V Positive Current-Sense Input. See 12SA+ function. Slot B 3.3V Auxiliary Output Enable. See AUXONA function. Slot B 12V And 3.3V Outputs Enable. See ONA function. Slot B Forced-On Input. See FONA function. Slot B Present-Detect Input. See PRES-DETA function. Overcurrent Timeout Programming Input. Connect a resistor between 500 and 500k from TIM to GND to program tFAULT. Leave TIM floating for a default timeout of 11ms. Digital Logic Gate Input Digital Output. 4ms debounced digital output of INPUT2. Digital Output. 4ms debounced digital output of INPUT1. Digital Logic Gate Input 12V Supply Input. V12VIN drives the gates of the MOSFETs connected to 3.3GA and 3.3GB. 12VIN powers an internal charge pump that drives the gates of the MOSFETs connected to 12GA and 12GB. Ground Power Ground. Connect externally to GND. Power-On-Reset Programming Input. Connect a resistor between 500 and 500k from PORADJ to GND to program the POR timing. Leave floating for a default value of 160ms.
MAX5946
Detailed Description
The MAX5946 dual hot-plug controller is designed for PCI express applications. The device provides hot-plug control for 12V, 3.3V, and 3.3V auxiliary supplies of two PCI express slots. The MAX5946's logic inputs/outputs allow interfacing directly with the system hot-plug-management controller or through an SMBus with an external I/O expander. An integrated debounced attention switch and present-detect signals are included to simplify system design. The MAX5946 drives four external n-channel MOSFETs to control the 12V and 3.3V main outputs. The 3.3V auxiliary outputs are controlled through internal 0.24 nchannel MOSFETs. Internal charge pumps provide a gate drive for the 12V outputs while the gate drive of the 3.3V output is driven by the 12V input supply. The 3.3V auxiliary outputs are completely independent from the main outputs with their own charge pumps.
At power-up, the MAX5946 keeps all of the external MOSFETs off until all supplies rise above their respective UVLO thresholds. The device keeps the internal MOSFETs off only until the 3.3VAUXIN supply rises above its UVLO threshold. Upon a turn-on command, the MAX5946 enhances the external and internal MOSFETs slowly with a constant gate current to limit the power-supply inrush current. The MAX5946 actively limits the current of all outputs at all times and shuts down if an overcurrent condition persists for longer than a programmable overcurrent timeout. Thermalprotection circuitry also shuts down all outputs if the die temperature exceeds +150C. After an overcurrent or overtemperature fault condition, the MAX5946L latches off while the MAX5946A automatically restarts after a restart time delay. The power requirement for PCI express connectors is defined by the PCI express card specification and summarized in Table 1.
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13
Dual PCI Express, Hot-Plug Controller MAX5946
RTIM RPORADJ
INPUT1 PWRGDA FAULTA TIM PORADJ
INPUT2
12VIN PWRGDB FAULTB
OUTPUT1
OUTPUT2
12SA+ RSENSE12A 12SA54mV + + 500mV CHARGE PUMP 5A 10A tFAULT OSCILLATOR A01 10A DEBOUNCE CHARGE PUMP 5A 500mV + + 54mV
12SB+
RSENSE12B 12SB-
12GA
12GB
tPOR OSCILLATOR 100mA
FAST OSCILLATOR A 0 0 1 100mA 150A MAX5946
150A
3.3SA+ 100mV RSENSE3.3A 3.3SA5A 20mV + + 100mV + + 20mV
3.3SB+ RSENSE3.3B 3.3SB-
3.3GA
50A 10A BIAS REFERENCES AND UVLO
3.3GB A 0 1 10A
CONTROL LOGIC MAIN-SLOT A 150mA
CONTROL LOGIC MAIN-SLOT B A051 150mA 150A
150A
3.3VAUXIN VREF CHARGE PUMP CONTROL LOGIC AUX-SLOT A CONTROL LOGIC AUX-SLOT B + VREF + CHARGE PUMP
3.3VAUXOA INPUT COMPARATORS AND CHIP-CONTROL LOGIC
3.3VAUXOB
PGND
GND
ONA
AUXONA
FONA
PRES-DETA
ONB
AUXONB
FONB
PRES-DETB
Figure 1. Functional Diagram
14
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Dual PCI Express, Hot-Plug Controller
Table 1. Power Requirements for PCI Express Connectors
POWER RAIL 3.3V Voltage Tolerance Supply Current Capacitive Load 12V Voltage Tolerance Supply Current Capacitive Load 3.3V AUXILIARY Voltage Tolerance Supply Current Wake Enabled 375mA (max) Non-Wake Enabled, Capacitive Load 9% (max) 375mA (max) 20mA (max) 150F (max) 9% (max) 375mA (max) 20mA (max) 150F (max) 9% (max) 375mA (max) 20mA (max) 150F (max) 9% (max) 3.0A (max) 1000F (max) 8% (max) 0.5A (max) 300F (max) 9% (max) 3.0A (max) 1000F (max) 8% (max) 2.1A (max) 1000F (max) 9% (max) 3.0A (max) 1000F (max) 8% (max) 5.5A (max) 2000F (max) X1 CONNECTOR X4/8 CONNECTOR X16 CONNECTOR
MAX5946
Table 2. Control Logic Truth Table
ON_ X X Low High Low High AUXON_ X X Low Low High High FON_ Low High High High High High PRES-DET_ X High Low* Low* Low* Low* 12V_ AND 3.3V_ OUTPUTS On Off Off On Off On 3.3VAUXO_ AUXILIARY OUTPUTS On Off Off Off On On
*PRES-DET_ high-to-low transition has a 4ms delay (tDEG).
Startup
The main supply outputs can become active only after all the following events have occurred: * V3.3VAUXIN is above its UVLO threshold * * * V 12VIN and V 3.3SA+ are both above their UVLO threshold ON_ is driven high PRES-DET_ is low for more than 4ms
The auxiliary supply output is made available only after the following events have occurred: * * * V3.3VAUXIN is above its UVLO threshold AUXON_ is driven high PRES-DET_ is low for more than 4ms
The FON_ input overrides all other control signals and turns on the respective slot when driven low, as long as the UVLO thresholds have been reached. Table 2 summarizes the logic conditions required for startup. The auxiliary supply input powers the internal control logic and analog references of the MAX5946, so the main supplies cannot be enabled if V3.3VAUXIN is not present. When an output is enabled, a programmable startup timer (tSU) begins to count the startup time duration. The value of tSU is set to 2x the fault timeout period (tFAULT). RTIM externally connected from TIM to GND sets the duration of tFAULT.
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15
Dual PCI Express, Hot-Plug Controller MAX5946
ON_, AUXON_ VON_,TH VPGTH12 VPGTH3.3 12G_, 3.3G_
VON_,TH ON_
12VO_, 3.3VO_
V12ILIM,TH RSENSE
12G_
12V OUTPUT CURRENT
VPGTH3.3AUX
3.3VAUXO_
3.3VAUXO_ PWRGD_
tPOR_HL PWRGD_ 3.3AUXIN RISING EDGE PWRGD_ IS PULLED UP TO 3.3. FAULT_ IS PULLED UP TO 3.3AUXIN. FAULT_
3.3VAUXIN RISING EDGE 2 x tFAULT
FAULT_ PWRGD_ IS PULLED UP TO 3.3VAUXO_. FAULT_ IS PULLED UP TO 3.3VAUXIN. A FAULT ON THE 3.3V OUTPUT OR 3.3VAUXO_ OUTPUT PRODUCES SIMILAR RESULTS.
Figure 2. Power-Up Timing, No Fault
Figure 3. 12V Power-Up Timing (Turn-On into Output Overcurrent/Short Circuit)
controller disengages both the 12V and 3.3V outputs for the particular slot (see the Fault Management section).
3.3V Auxiliary Output Normal Operation
12G_ V12ILIM,TH RSENSE 12V OUTPUT CURRENT PWRGD_
The auxiliary output current is internally monitored and actively limited to the maximum current-limit value. An overcurrent fault condition occurs when the output current exceeds the overcurrent threshold for longer then tFAULT. A fault on an auxiliary channel causes all supplies of the affected channel to be disabled after a programmable time period t FAULT (see the Fault Management section).
P Power-Good (PWRGD_)
tFAULT
FAULT_ PWRGD_ IS PULLED UP TO 3.3VAUXO_. FAULT_ IS PULLED UP TO 3.3VAUXIN. A FAULT ON THE 3.3V OUTPUT OR 3.3VAUXO_ OUTPUT PRODUCES SIMILAR RESULTS.
Figure 4. 12 Output Overcurrent/Short Circuit During Normal Operation
Power-good (PWRGD_) is an open-drain output that pulls low a time (tPOR_HL) after all of the outputs of the respective slot are fully on. All outputs are considered fully on when 3.3G_ has risen to VPGTH3.3, 12G_ has risen to V PGTH12 , and V 3.3AUXO_ is less then V PGTH3.3AUX . t POR_HL is adjustable from 2.5ms to 1.5s by connecting a resistor from PORADJ to GND. See the Setting the Power-On-Reset Timeout Period (tPOR) section.
12V and 3.3V Outputs Normal Operation
The MAX5946 monitors and actively limits the current of the 12V and 3.3V outputs after the startup period. Each output has its own overcurrent threshold. If any of the monitored output currents rise above the overcurrent threshold for a period tFAULT, FAULT_ asserts and the
16
Thermal Shutdown
When the die temperature goes above (TSD) +150C, an overtemperature fault occurs and the MAX5946 shuts down all outputs. The device waits for the junction temperature to decrease below TSD - Hysteresis before entering fault management (see the Fault Management section).
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Dual PCI Express, Hot-Plug Controller
FAULT Management
A fault occurs when an overcurrent lasts longer then tFAULT or when the device experiences an overtemperature condition. * A fault on a main output (12V or 3.3V) shuts down both main outputs of the respective slot. The 3.3V auxiliary is not affected. A fault on the 3.3V auxiliary output shuts down all three outputs of the respective slot. 4ms debounced time. When the card is removed, an internal 50k pullup forces PRES-DET_ high and the respective slot is shut down with no delay. PRES-DET_ works in conjunction with ON_ and VAUXON_ and only enables the device when ON_ and VAUXON_ are high. A logic-low on FON_ forces the respective slot (main supplies and auxiliary) to turn on regardless of the status of the other logic inputs provided the UVLO thresholds are exceeded on all of the inputs.
MAX5946
*
The MAX5946A automatically restarts from a fault shutdown after the tRESTART period, while the MAX5946L latches off. If an overcurrent fault occurred on a main output, bring ON_ low for at least tRESET (100s) and high again to reset the fault and restart the outputs. If the overcurrent fault occurred on an auxiliary output or an overtemperature fault occurred, bring both ON_ and AUXON_ low for a minimum of tRESET to reset the fault. Bring ON_ and/or AUXON_ high again to restart the respective outputs. As an extra protection, the MAX5946L waits a minimum of tRESTART before it can be restarted.
Active Current Limits
Active current limits are provided for all three outputs of slot A and slot B. Connect a current-sense resistor between 12S_+ and 12S_- to set the current limit for the 12V outputs. The current limit is set to 54mV/RSENSE12. RSENSE12 is either R1 or R3 in the Typical Application Circuit. Connect a current-sense resistor between 3.3S_+ and 3.3S_- to set the current limit for the 3.3V main outputs to 20mV/RSENSE3.3. RSENSE3.3 is either R2 or R4 in the Typical Application Circuit. For the auxiliary output (3.3VAUXO_) the current limit is fixed at 470mA. When the voltage across R SENSE12 or R SENSE3.3 reaches the current-limit threshold voltage, the MAX5946 regulates the gate voltage to maintain the current-limit threshold voltage across the sense resistor. If the current limit lasts for tFAULT then an overcurrent fault occurs. The MAX5946_ shuts down both the 12V and 3.3V outputs and asserts the FAULT_ output of the respective slot. When the auxiliary output reaches the current limit (470mA) for longer then tFAULT, a fault occurs and the device shuts down all outputs and asserts FAULT of the respective slot.
Debounced Logic Gate (Input_ and Output_)
INPUT1 and INPUT2 accept inputs from mechanical switches. The corresponding outputs are OUTPUT1 and OUTPUT2. OUTPUT_ is debounced for 4ms. When INPUT_ goes from high to low, OUTPUT_ goes low right away and stays low for at least 4ms. After the debounce time OUTPUT_ follows INPUT_. If INPUT_ goes from low to high, OUTPUT_ goes high right away and stays high for at least 4ms. After the debounce time, OUTPUT_ follows INPUT_. Figure 5 shows the timing diagram describing the INPUT_/OUTPUT_ debounced feature.
Undervoltage Lockout Threshold
The UVLO thresholds prevent the internal auxiliary MOSFETs and the external main channel MOSFETs (Q1-Q4 in the Typical Application Circuit) from turning on if V12VIN, V3.3VIN, and V3.3VAUXIN are not present. Internal comparators monitor the main supplies and the auxiliary supply and keep the gate-drive outputs (12GA, 12GB, 3.3GA, and 3.3GB) low until the supplies rise above their UVLO threshold. The 12V main supply is monitored at 12VIN and has a UVLO threshold of 10V. The 3.3V main supply is monitored at 3.3SA+ and has a UVLO threshold of 2.65V. The auxiliary supply is monitored at 3.3VAUXIN and has a 2.65V UVLO threshold. For either main channel to operate, V3.3VAUXIN must be above its UVLO threshold.
Present-Detect and Forced-On Inputs P (PRES-DET_, FON_)
PRES-DETA and PRES-DETB inputs detect the PRSNT#2 pin on a PCI express connector. When the card is plugged in, PRES-DET_ goes low and allows the turn-on of the outputs of the respective slot after a
INPUT tDBC DEBOUNCED OUTPUT tDBC tDBC
Figure 5. INPUT_ and OUTPUT_ Debounced Feature ______________________________________________________________________________________ 17
Dual PCI Express, Hot-Plug Controller MAX5946
SHUT DOWN 12V AND 3.3V OUTPUTS. ASSERT FAULT_ STAY WAITING FOR tRESTART Y HAS tFAULT ELAPSED? START COUNTING tFAULT Y WAS CURRENT LIMIT DETECTED ON ANY 12V OR 3.3V OUTPUT? 12V AND 3.3V OUTPUTS ARE ENABLED
N N
IS FAULT STILL PRESENT?
Y
N RESET tFAULT COUNTER Y LATCH-OFF OPTION? N
STAY WAITING FOR ON_ TRANSITION HIGH->LOW->HIGH
RESET FAULT_ AND RESTART 12V, 3.3V SUPPLIES N POWER-ON MAIN SUPPLIES FAULT AND PWRGD ARE HIGH IMPEDANCE ENABLE CHARGE ON 12G_ AND 3.3G_ PINS. START COUNTING tSU
3.3AUXIN IS ON AND ABOVE UVLO
HAS tSU ELAPSED?
Y
ARE PWRGD THRESHOLDS REACHED?
N
RESET PWRGD_ AFTER tPOR_LH DELAY
Y
STAY WAITING FOR BOTH ON_ AND AUXON_ TRANSITION HIGH->LOW->HIGH
RESET FAULT_ AND RESTART ALL SUPPLIES
ASSERT PWRGD_ AFTER tPOR_HL DELAY
N Y POWER-ON AUXILIARY SUPPLIES FAULT AND PWRGD ARE HIGH IMPEDANCE ENABLE CHARGE ON INTERNAL AUXILIARY MOSFET, BEGIN COUNTING tSU
HAS tSU ELAPSED?
Y
LATCH-OFF OPTION?
N
SHUT DOWN ALL OUTPUTS, ASSERT FAULT_, STAY WAITING FOR tRESTART ELAPSED.
Y
IS tFAULT ELAPSED?
START COUNTING tFAULT
Y
WAS CURRENT LIMIT DETECTED ON AUXILIARY OUTPUT?
AUX SUPPLY OUTPUT IS ENABLED
N
N
IS FAULT STILL PRESENT?
Y
N RESET tFAULT COUNTER
Figure 6. Fault Management Flow Chart 18 ______________________________________________________________________________________
Dual PCI Express, Hot-Plug Controller
External MOSFET Gate Drivers (12GA, 12GB, 3.3GA, and 3.3GB)
The gate drive for the external MOSFETs is provided at 12GA, 12GB, 3.3GA, and 3.3GB. 12G_ is the gate drive for the 12V main supply and is boosted to 5.3V above V12VIN by an internal charge pump. During turn-on, 12G_ sources 5A into the external gate capacitance to control the turn-on time of the external MOSFET. During turn-off, 12G_ sinks 150A from the external gate capacitance to quickly turn off the external MOSFET. During short-circuit events, an internal 100mA current activates to rapidly bring the load current into the regulation limits. 3.3G_ is the gate drive for the 3.3V main supply's MOSFET and is driven to 5.5V above the 3.3V main supply. The power for 3.3G_ is supplied from 12VIN and has no internal charge pump. During turn-on, 3.3G_ sources 5A into the external gate capacitance to control the turn-on time of the external MOSFET. During turn-off, 3.3G_ sinks 150A to quickly turn off the external MOSFET. During short-circuit events, an internal 150mA current activates to rapidly turn off the appropriate external MOSFET.
MAX5946
V x CLOAD t SU GATE ICHG where tSU = 2 x tFAULT and where 1) ICHG = 5A. 2) V GATE = 18.4V for 12G_ and V GATE = 9.4V for 3.3G_. 3) CLOAD is the total capacitance load at the gate. Maximum and minimum values for RTIM are 500 and 500k, respectively. Leave TIM floating for a default tFAULT of 11ms.
Setting the Power-On-Reset Timeout Period (tPOR_HL)
tPOR_HL is the time from when the gate voltages of all outputs of a slot reach their power-good threshold to when PWRGD_ pulls low. Program the power-on-reset timeout period (tPOR) by connecting a resistor (RPORADJ) from PORADJ to GND. tPOR_HL can be calculated by the following equation: tPOR_HL = 2.5s / x RPORADJ Maximum and minimum values for RPORADJ are 500 and 500k, respectively. Leave PORADJ floating for a default tPOR of 160ms.
Auxiliary Supply (3.3VAUXIN)
3.3VAUXIN provides power to the auxiliary outputs as well as the internal logic and references. The drains of the internal auxiliary MOSFETs connect to 3.3VAUXIN through internal sense resistors and the sources connect to the auxiliary outputs (3.3VAUXOA and 3.3VAUXOB). Both MOSFETs have typical on-resistance of 0.3. An internal charge pump boosts the gate-drive voltage to fully turn on the internal n-channel MOSFETs. The auxiliary supplies have an internal current limit set to 470mA.
Component Selection
Select the external n-channel MOSFET according to the applications current requirement. Limit the switch power dissipation by choosing a MOSFET with an RDS_ON low enough to have a minimum voltage drop at full load. High RDS_ON causes larger output ripple if there are pulsed loads. High RDS_ON can also trigger an external undervoltage fault at full load. Determine the MOSFETs power rating requirement to accommodate a short-circuit condition on the board during startup. Table 3 lists MOSFETs and sense resistor manufacturers.
Applications Information
Setting the Fault Timeout Period (tFAULT)
tFAULT is the time an overcurrent or overtemperature fault must remain for the MAX5946 to disable the main or auxiliary channels of a particular slot. Program the fault timeout period (tFAULT) by connecting a resistor (RTIM) from TIM to GND. tFAULT can be calculated by the following equation: tFAULT = 166ns / x RTIM The tFAULT programmed time duration must be chosen according to the total capacitance load connected to the 12G_ and 3.3G_ pins. To properly power-up the main supply outputs, the following constraints need to be taken:
Additional External Gate
External capacitance can be added from the gate of the external MOSFETs to GND to slow down the dV/dt of the 12V and 3.3V outputs.
Maximum Load Capacitance
Large capacitive loads at the 12V output, the 3.3V output, and the 3.3V auxiliary output can cause a problem when inserting discharged PCI cards into live backplanes. A fault occurs if the time needed to charge the capacitance of the board is greater than the typical startup time (2 x tFAULT). The MAX5946 can withstand
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19
Dual PCI Express, Hot-Plug Controller MAX5946
Table 3. Component Manufacturers
COMPONENT Sense Resistor MANUFACTURER Vishay-Dale IRC Fairchild MOSFETs International Rectifier Motorola Vishay-Siliconix PHONE 402-564-3131 704-264-8861 888-522-5372 310-322-3331 602-244-3576 -- WEBSITE www.vishay.com www.irctt.com www.fairchildsemi.com www.irf.com www.mot-sps.com/ppd/ www.vishay.com
large capacitive loads due to their adjustable startup times and adjustable current-limit thresholds. Calculate the maximum load capacitance as follows: t xI CLOAD < SU LIM VOUT VOUT is either the 3.3V output, the 12V output, or the 3.3V auxiliary output for slot A or slot B.
thresholds before startup can occur. Input transients can cause the input voltage to sag below the UVLO threshold. The MAX5496 rejects transients on the input supplies that are shorter than 4s typical.
Chip Information
TRANSISTOR COUNT: 10,487 PROCESS: BiCMOS
Input Transients
The 12V input (12VIN), the 3.3V input (3.3SA+), and the 3.3V auxiliary (3.3VAUXIN) must be above their UVLO
20
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Dual PCI Express, Hot-Plug Controller
Typical Application Circuit
PCI EXPRESS SLOT A PRSNT1 +12V 1F Q1 SI7448DP-T1 V12VIN IN5819 R1 8m V3.3AUXIN R3 8m Q3 SI7448DP-T1 PRSNT1 +12V PCI EXPRESS SLOT B ADD-IN CARD
MAX5946
0.1F
12SA-
12SA+
112SB-
3.3VAUXIN
12SB+
12VIN
12GA
12GB
GND PWRGD 10k PWRGDA
GND PWRGDB 10k PWRGD
MAX5946 3.3VAUX 3.3VAUXOA 3.3VAUXOB RPORADJ = OPEN GND PORADJ 3.3VAUX
OUTPUT1 / OUTPUT2
AUXONA / AUXONB
FAULTA / FAULTB
INPUT1 / INPUT2
FONA / FONB
PRES-DETA
PRES-DETB
ONA / ONB
3.3SA+
3.3SB+
3.3SA-
3.3SB-
3.3GA
RTM = OPEN Q2 SI7448DP-T1 +3.3V 2 PRSNT2 V3.3AUXIN 2 2 2 ATTENTION SWITCHES 3.3V INPUT 0.1F PRSNT2 R2 5m 2 2 R4 5m Q4 SI7448DP-T1 +3.3V
10k
MRL LED's
MAX7313ATG 16-BIT I/O EXPANDER 2 2
MRL LED's
2 SMBus
3 AO-2 INT
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3.3GB
TIM
21
Dual PCI Express, Hot-Plug Controller MAX5946
Package Information
(The package drawing(s) in this data sheet may not reflect the most current specifications. For the latest package outline information, go to www.maxim-ic.com/packages.) 36L,40L, QFN.EPS 22 ______________________________________________________________________________________
Dual PCI Express, Hot-Plug Controller
Package Information (continued)
(The package drawing(s) in this data sheet may not reflect the most current specifications. For the latest package outline information, go to www.maxim-ic.com/packages.)
MAX5946
U
Maxim cannot assume responsibility for use of any circuitry other than circuitry entirely embodied in a Maxim product. No circuit patent licenses are implied. Maxim reserves the right to change the circuitry and specifications without notice at any time.
Maxim Integrated Products, 120 San Gabriel Drive, Sunnyvale, CA 94086 408-737-7600 ____________________ 23 (c) 2004 Maxim Integrated Products Printed USA is a registered trademark of Maxim Integrated Products.

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